Asphalt is a complex colloid comprised of asphaltenes suspended in oils and resins commonly referred to as the maltene fraction. The chemical composition of the maltene fraction has a significant effect on the penetration, softening point, and viscosity of asphalt as lighter components are converted into larger molecules.
Crude oils are a naturally occurring complex mixture composed predominantly of hydrogen and carbon containing compounds. They vary widely in relative amounts and characteristics of different hydrocarbons. There are various systems for classification of crude oil. One such system classifies oil as paraffin, asphaltic (naphthenic), or mixed-based depending upon the type of hydrocarbon present in the crude. Alternatively, crude oil may be classified as heavy crude (20-25 API gravity), refining crude (25-35 API gravity) or light crude (35-40 API gravity). Heavy crudes (20-25 API gravity) are favored for production of asphalts because these crudes are rich in asphaltenes.
Petroleum asphalt may not conform to paving or industrial grade specifications and air blowing may be used to prepare the asphalt material for paving and roofing applications. The air blowing process includes bubbling air through an asphalt mixture to oxidize some of the constituents. Additionally, air blowing may also include the use of a catalyst to accelerate reactions.
In U.S. Pat. No. 7,951,239, Trumbore describes the secondary addition of a wax to increase the softening point of non-coating grade asphalt to provide a penetration that is near the target of 15 dmm. Further, Trumbore requires careful monitoring to prevent the penetration from dropping below the target penetration of 15 dmm during the oxidation process to meet both the penetration and softening point specification of ASTM 3462.